This invention relates in general to rain gauges and in particular to fully automatic and electronic rain gauges.
There have been a variety of attempts at developing a fully automatic rain gauge, most all of which utilize moveable mechanical parts which exhibit certain inherent limitations and tradeoffs. The basic problem to overcome in achieving a fully automatic rain gauge is the removal of very small volumes of water from the collector, incrementally, while maintaining a high degree of repeatability in the amount of each volume removed. Each removal can then be sensed and converted into a rainfall amount. Most all rain gauges commercially available today utilize a mechanical means to achieve the transfer of water in equal volumes. The disadvantages inherent in the mechanical means are size, expense, and rangeability, whereas the present invention overcomes these disadvantages due to its non-mechanical approach.
The most widely used approach in the market place today is the mechanical tipping bucket (inventors; Gerald Kahl and Guide Guideili Guidi, U.S. Pat. No. 3,705,533). The rain gauge basically consists of a collector and a series of funnels to divert the rain water to a tipping bucket mechanism. The collector and tipping bucket mechanism are so designed that each hundreth of an inch of rainfall causes the alternate fill and tip of the mechanism. A sealed glass enclosed mercury switch or similar is attached to the mechanism so that an electrical pulse is generated with each tip of the bucket.
The disadvantage of this approach is in the size required by the collector, which is typically 10 inches in diameter, due to the fact that the tipping bucket assembly requires over 25 thousanths of a cubic inch to cause tipping action. The tradeoff is that at a heavier rainfall rate, for example a 5 to 7 inch per hour rate, the tipping bucket approach will exhibit a 3% to 4% error in its precision due to its inability to transfer relatively large volumes of water.
The present invention, which incorporates a nonmechanical means to accomplish the water transfer, requires a collector no larger than 2 inches in diameter. This is a reduction in collector size of approximately 80% over the tipping bucket method. Also due to the small collector size and extremely low volumes of water transfer, a high degree of resolution in measurement can be achieved, over a wide range of rainfall rates. A resolution of 0.003 inch increments can be attained accurately over a range of 0.01 to 10.00 inches per hour rainfall rates.
Other mechanical means have been adapted such as the rotary bucket mechanism (inventor; James Mink, U.S. Pat. No. 3,958,457) which senses the level of water in a column and at a predetermined level activates a motor which turns the rotary bucket and thus removes an equal volume of water incrementally, and the paristalic pump mechanism (inventor; Colin Lucas, U.S. Pat. No. 3,721,122) which senses the level of water collected and at a predetermined level activates the pump and thus removes an equal volume of water incrementally.
Both of these methods exhibit similar inherent limitations as the tipping bucket method though with one additional disadvantage, and that being the power required for operation. The majority of power being consumed by the motor in the rotary bucket method and the pump in the paristalic pumping method. This makes the method energy inefficient, less practical for remote applications, and lacking in easy portability. The present invention by contrast, requires extremely low amounts of current for operation due to the sensing network utilized in conjunction with Complemenatary Metal Oxide Semiconductor technology (CMOS Integrated Circuitry). The sensing network is designed so that when an equal volume of water is discharged, the resistance of the rain water is detected by the sensing network, which is typically between 100,000 and 200,000 ohms, and then applied to the gate of a CMOS integrated circuit, causing the associated circuitry to "trigger". This approach virtually eliminates the need for amplifying the sensor signals which all other electronic rain gauges require. As a result then of the sensing method employed, and the unique application of CMOS integrated circuitry, this present invention could function on very small batteries for several months, making it highly energy efficient, easily adaptable for remote use, portable, and independent of power failures that could occur during a storm.